I am not sure if it will work but you can surely try the following steps:
2.In the window that pops up remove all the entries that are shown under NTP SERVERS.Then give add and add the IPs of the other three rhel systems.
3.select the SHOW ADVANCED OPTIONS tab and tick the option SYNCHRONIZE SYSTEM CLOCK and untick the option USE LOCAL TIME.
3.In the TIMEZONE tab make sure you have selected the correct timezone and tick the option SYSTEM USES UTC.
4.Do the above steps in each of the systems,changing the IP as required in each system.
LOGOUT AND RESTART and check if the 4 systems time is the same.Please let me know if it worked or not.